1. Field of the Invention
The present invention relates to an illumination apparatus suitable for illuminating a rectangular object such as a liquid crystal panel, and a liquid crystal projector using such an illumination apparatus.
2. Description of the Related Art
As for an illumination optical system for uniformly illuminating a rectangular object such as a liquid crystal panel, an integrator optical system in which two fly-eye lens-arrays are combined is known from, for example, Japanese Laid-Open Patent Application No. 3-111806.
The integrator optical system shown in the above patent application divides a luminous flux originating from a light source with a reflector such as a parabolic reflector, an ellipsoidal reflector and a hyperbolic reflector, by multiple rectangular focusing lenses constituting a first fly-eye lens-array to form secondary light source images. A convolution of the secondary light source images is imaged on one illuminated object through a second fly-eye lens-array having multiple focusing lenses corresponding to the multiple rectangular focusing lenses of the first fly-eye lens-array. According to such an integrator optical system, it is believed that intensity distribution of light on a surface of the illuminated object can be made almost uniform as well as usability of light from the light source being improved. Particularly, the usability of light and uniformity of intensity distribution can be improved by matching shapes of respective focusing lenses of the first and the second fly-eye lens-array to an aspect ratio of the rectangular illuminated object, for example, by making the focusing lens into a rectangular shape having the ratio of a long side and a short side of 4:3.
That is, in Japanese Laid-Open Patent Application No.3-111806, an integrator optical system using a first macro-lens array, of which the common name is fly-eye lens plate, having rectangular lenses on a first lens plate and a second macro-lens array having lenses corresponding to the lenses on the first lens plate can make illumination matching an aspect ratio of an illuminated object. Then, as for an example of a configuration at the light source side in order to make the size of the integrator optical system compact, a light source is placed at a first focal point of an ellipsoidal mirror, a collimator lens is located behind a second focal point of the mirror, and an integrator optical system is arranged behind the collimator lens, as shown in FIG. 1 that is also drawn in Japanese Laid-Open Patent Application No.3-111806.
Also, FIG. 2 shows a configuration example including a parabolic mirror instead of the ellipsoidal mirror shown in FIG. 1.
In FIG. 1 and FIG. 2, basically, illumination with an aspect ratio suitable for a liquid crystal panel 103 as an illuminated object is performed using a first macro-lens array or a first fly-eye lens-array 101 having rectangular lenses on a first lens plate in an integrator optical system 100 and a second macro-lens array or a second fly-eye lens-array 102 having lenses respectively corresponding to the rectangular lenses of the first fly-eye lens-array.
Then, at the light source side of the configuration shown in FIG. 1, light generated from a light source 105 arranged at a first focal point F1 of an ellipsoidal mirror 104 as a reflector, is reflected from the ellipsoidal mirror 104, and is focused to a second focal point F2, and enters the integrator optical system 100 by a collimator lens 107.
Also, at the light source side of the configuration shown in FIG. 2, light generated from a light source 105 arranged at a focal point F1 of a parabolic mirror 104 as a reflector is reflected from the surface of the parabolic mirror 104, collimated, focused to a point corresponding to a second focal point F2 of an ellipsoid having a first focal point at F1 by a convex lens 106, then enters the integrator optical system 100 by a collimator lens 107.
Herein, in FIG. 1 and FIG. 2, a polarization alignment prism array for aligning polarization of light generated from the light source with a mixture of a p-polarization component and a s-polarization component to only the s-polarization component or the p-polarization component is indicated with the numeral 108. Two lenses are also indicated with the numerals 109 and 110 in the FIG. 1 and FIG. 2.
According to the configuration example shown in FIG. 2, although the number of the members is one more than that of the example shown in FIG. 1, the size of a reflector and the position of a focal point of the reflector, which represents a parabolic mirror and an ellipsoid mirror, etc., can be freely defined.
Also, according to Japanese Laid-Open Patent Application No.10-161065, an illumination apparatus is proposed, in which a collimated light obtained from a light source placed at a focal point of a parabolic mirror is focused by a convex lens, collimated again by a concave lens and led to a polarization conversion means or an integrator optical system in order to decrease the size of the integrator optical system.
FIG. 3 shows an illumination apparatus based on the idea of Japanese Laid-Open Patent Application No. 10-161065. As compared with the illumination apparatus shown in FIG. 2, a collimating lens 111 is arranged at the near side or light source side of a point corresponding to a second focal point F2 of an ellipsoid having a first focal point at F1, wherein the collimator lens 107 is omitted.
Furthermore, according to Japanese Laid-Open Patent Application No. 5-264904, as shown in FIG. 4, similar to the case of the above mentioned Japanese Laid-Open Patent Application No. 3-111806, it is proposed that light generated from a light source 105 placed at a first focal point F1 of an ellipsoidal mirror 104 or a parabolic mirror is led to an integrator optical system 100 through a collimator lens 107 arranged behind a second focal point F2. Luminous flux not reflected by the surface of the ellipsoidal mirror 104 returns to the light source 105 using a concave mirror 112 having a spherical center at the first focal point F1. Thus most of the luminous flux generated from the light source 105 can be utilized.
Also, according to Japanese Laid-Open Patent Application No. 2001-66697, as shown in FIG. 5, it is proposed that a reflection film 214 on a part of a vessel 213 of a lamp 212 attached to a reflector 211 is formed to be a light source having a substantially spherical mirror structure so that the luminous flux generated from the light source is returned toward the reflector 211 side to be effectively utilized.
The idea shown in the aforementioned Japanese Laid-Open Patent Application No.3-111806 or in FIG. 1 and FIG. 2 is that luminous flux originating from the light source 105 is focused at once and collimated by the collimator lens 107 to decrease the whole size of the integrator optical system 100, thus achieving the comprehensive object. However, according to the configuration, the size of an image of the light source at the focal point, at which luminous flux originating from the light source 105 is focused again, is magnified to several times of the size of the original image of the light source and collimation by a collimator lens 107 is limited so that usability of light in the integrator optical system 100 is lowered. The property in the case of use of an ellipsoidal mirror instead of the parabolic mirror 104 shows the same tendency as the case of the combination of the parabolic mirror 104 and the convex lens 107.
Furthermore, in the case of the configuration example shown in FIG. 1, as a coverage angle θ of the ellipsoidal mirror 104 is increased, a maximum incidence angle Ψ is also increased, so that efficiency at the collimator lens is reduced and the illumination apparatus becomes complex because of needing many lenses, etc.
Also in the case of the configuration as shown in Japanese Laid-Open Patent Application No.10-161065 or in FIG. 3, in principle, collimated light exiting from the collimating lens 111 that is a concave-lens has the same degree of collimation as collimated light obtained by use of the collimator lens 107 shown in FIG. 2. As similar to the aforementioned example in the prior art, even if an ellipsoidal mirror is employed and the collimating lens 111 is placed at the near side of the second focal point. F2, the property shows a same tendency as the case of the combination of the parabolic mirror 104 and the collimating lens 111.
Moreover, in the case of Japanese Laid-Open Patent Application No. 5-264904 like the example shown in FIG. 4, the concave mirror 112 having a spherical center at the first focal point F1 is arranged and light not covered by the surface of the parabolic mirror 104 is reflected and utilized to improve the usability of the luminous flux generated from the light source 105. However, the idea that luminous flux is focused at once and collimated by the collimator lens 107 to decrease the whole size of the integrator optical system 100, thus achievement of the comprehensive object is the same idea as the example in the prior art shown in FIG. 1. Hence, similar to the configuration shown in FIG. 1, the size of an image of the light source at the focal point, at which luminous flux emitted from the light source 105 is focused again, is magnified to several times of the size of an original image of the light source and collimation by a collimator lens is limited so that light usability of the integrator optical system 100 is lowered.
Furthermore, the configuration example shown in FIG. 4 is similar to the case of Japanese Laid-Open Patent Application NO. 3-111806 in that as a coverage angle θ of the ellipsoidal mirror 104 is increased, a maximum incidence angle Ψ is also increased, so that efficiency at the collimator lens is reduced and an illumination apparatus becomes complex because of needing many lenses, etc.
Also, in the case of Japanese Laid-Open Patent Application No.2001-66697 like the example shown in FIG. 5, light reflected from a spherical mirror magnifies an arc image of the light source as if there were a group of arc images at the position away from the same degree of a distance from the vessel center to the mirror as indicated by dashed lines in FIG. 5. In other word, since the arc image is present at a position away from the focal point of the reflector, it is disadvantageous that parallelism of luminous flux from the reflector 211 obtained via the spherical reflection mirror is extremely lowered as compared to light directly coming from the arc. Moreover, at a pipe wall reaching to near 1000° C., reflection property is lowered for a short time period. Even if the lamp is slightly floated from the pipe wall as shown in FIG. 6, degradation time of the lamp may become slightly longer, but the lamp must be frequently exchanged in practice.